Calculation - Torque required for a motor

[BenzT]

Hi,



Object with a weight of W2 kg has to be moved and positioned at any degrees from 0 to 360. So i used a arm with a length L1 and weight W1 to carry the object.

I am not rotating parallel to the floor or ground. Its against the gravity like a giant wheel...

How do i select a motor based on some or all of the given parameters ( Torque,Gear Ratio,Power On...)

Pls give any formulas, Weblinks, Documents to know the details about it...

 

[FvM]

For torque calculation, read a physics school book.

Maxim torque (in horizontal position) is

Tmax = L1 * (0.5*W1 + W2)

Consider that physic book calculates with mass and gravity constant instead of "weight".

Tmax = L1 * g * (0.5*m1 + m2)

Gear ratio and power calculates according to (unsaid) speed specification.

 

[KlausST]

Hi,

You need to take acceleration into account. (including motor inertia)
Also add some margin.

Klaus

 

[BenzT]

For torque calculation, read a physics school book.

Maxim torque (in horizontal position) is

Tmax = L1 * (0.5*W1 + W2)

I have asked for the vertical direction. I think, in order to rotate and position at different angle, the motor will require torque depends on the angulation.

I need the formula, if i position the object at 0 degree, 30 degree, 190 degree and like that...

 

[FvM]

I have asked for the vertical direction. I think, in order to rotate and position at different angle, the motor will require torque depends on the angulation.

You are thinking right. I calculated maximum torque because it sets the motor power requirements. There's a simple sin(phi) factor for other positions.

Is it asking too much to reopen the school book?

 

[BradtheRad]

against the gravity like a giant wheel

It's common to add a counterweight, so that you can use a smaller, less powerful motor.

 

[BenzT]

It's common to add a counterweight, so that you can use a smaller, less powerful motor.

As per my application, i can not supposed to add counter weight here.

I failed to mention one thing here. W2 will be 3 times higher weight than W1

 

[c_mitra]

As per my application, i can not supposed to add counter weight here...

I presume you understand what a torque is. Your motor will act unbalanced if the center of gravity (or center of mass) of the rotating body does not fall on the motor axis of rotation.

Most common motors are not designed for unbalanced load; you will get a noise like your mobile on the vibration mode.

 

[BenzT]

I have seen some robotic arms where they are having some motor at the joints. The load has been accessed by an ARM from that joint. The ARM is not supposed to have the counter weight there..

 

[FvM]

Yes, it's possible to design the drive without a counter weight. Motor and gear must provide respectively more power and torque. The motor controller must be aware of the torque variations during movement, it may be necessary to break the drive actively to hold a position.

Said robotic arms have powerful motors and high dynamic controls with encoder feedback to manage the situation.

 

[c_mitra]

I have seen some robotic arms where they are having some motor at the joints. The load has been accessed by an ARM from that joint. The ARM is not supposed to have the counter weight there..

That can only be achieved with gears with large ratios so that the friction can lock the arm. Of course the motion will be slow...